In recent years, there has been developed an optical element in which porous silicon is formed to be used as a light emitting element. Japanese Laid-Open Patent Publication No. 4-356977 discloses such an optical element, in which a large number of micro-pores 102 are formed in the surface region of a silicon substrate 101 by anodization, as shown in FIG. 33. If the porous silicon is irradiated with light, photo-luminescence having its absorption edge in the visible region is observed, which implements a light-receiving/light-emitting element using silicon. That is, in a normal semiconductor apparatus composed of single-crystal silicon, an excited electron makes an indirect transition to a lower energy level so that the energy resulting from the transition is converted into heat, which renders light emission in the visible region difficult. However, there has been reported a phenomenon that, if silicon has a walled structure, such as porous silicon, and its wall thickness is about 0.01 xcexcm, the band width of the silicon is enlarged to 1.2 to 2.5 eV due to the quantum size effects, so that an excited electron makes a direct transition between the bands, which enables light emission.
It has also been reported that two electrodes are provided on both ends of the porous silicon so that electroluminescence is observed by the application of an electric field.
However, if electroluminescence is to be obtained by the application of an electric field or photoluminescence is to be obtained by the irradiation with light of the porous silicon formed by anodization in the surface region of the silicon substrate 101 as shown in FIG. 33, the following problems are encountered.
That is, the diameter and depth of the micro-pore 102 formed by anodization are difficult to control. In addition, the configuration of the micro-pore 102 is complicated and the distribution of its wall thickness is extremely random. As a result, if etching is intensely performed in order to reduce the wall thickness, the wall portions may be partially torn and peeled off the substrate. Moreover, since the distribution of the wall thickness is random, the quantum size effects are not generated uniformly over the whole wall portions, so that light emission with a sharp emission spectrum cannot be obtained. Furthermore, the wall surface of the micro-pore in the porous silicon readily adsorbs molecules and atoms during anodization, due to its complicated configuration. Under the influence of the atoms and molecules attached to the surface of the silicon, the resulting optical element lacks the capability of reproducing a required emission wavelength and its lifespan is also reduced.
On the other hand, with the development of the present information-oriented society, a semiconductor apparatus in which a semiconductor integrated circuit is disposed has presented an increasing tendency toward the personalization of advanced info-communication appliances with large capacities. In other words, there has been a demand for appliances which enable advanced information transmission to and from a hand-held computer or cellular phone. To meet the demand, it is required to not only enhance the performance of the conventional semiconductor apparatus, which processes only electric signals, but also implement a multi-function semiconductor apparatus which processes light, sounds, etc., as well as electric signals. FIG. 34 shows the cross sectional structure of a three-dimensional integrated circuit system that has been developed in order to satisfy the requirements. Such a three-dimensional integrated circuit system is expected to surmount the miniaturization limit inherent in the conventional two-dimensional integrated circuit system as well as improve and diversify functions to be performed. In the drawing, a PMOSFET 110a consisting of a source 103, a drain 104, a gate oxide film 105, and a gate 106 is formed in the surface region of an n-well 102, which is formed in a p-type silicon substrate 101a as a first layer. In the surface region of the first-layer silicon substrate 101a are formed semiconductor apparatus including an NMOSFET 110b consisting of the source 103, drain 104, gate oxide film 105, and gate 106. There are also formed a connecting wire 107 between the source and drain regions and an inter-layer insulating film 108 for covering each region, which has been flattened. On the inter-layer insulating film 108 is formed a second-layer silicon substrate 101b made of single-crystal silicon. On the second-layer silicon substrate 101b are also formed semiconductor apparatus such as the PMOSFET 110a and NMOSFET 110b, similarly to the semiconductor apparatus on the above first-layer silicon substrate 101a. The semiconductor apparatus in the first layer and the semiconductor apparatus in the second layer are electrically connected via a metal wire 109 (see, e.g., xe2x80x9cExtended Abstracts of 1st Symposium on Future Electron Devices,xe2x80x9d p.76, May 1982).
However, such a three-dimensional integrated circuit system has the following problems. The wire 109 is formed by a deposition method in which, after a contact hole was formed, a wiring material is deposited and buried in the contact hole. Since the resulting contact hole becomes extremely deep, deficiencies such as an increase in resistance value and a break in wiring are easily caused by a faulty burying of the wiring material, resulting in poor reliability. With such problematic manufacturing technology, it is difficult to implement a three-dimensional integrated circuit system which can be used practically. In particular, it is extremely difficult to implement an integrated circuit system in more than three dimensions.
The present invention has been achieved by focusing on the fact that, if a structure in which a large number of semiconductor micro-needles are arranged is used instead of a porous structure, the diameters of the semiconductor micro-needles become uniform. It is therefore a first object of the present invention to provide a quantized region for implementing intense light emission with a narrow wavelength distribution, such as electroluminescence or photoluminescence, and conversion of optical signals to electric signals.
A second object of the present invention is to provide a semiconductor apparatus with an advanced information processing function by incorporating an aggregate of semiconductor micro-needles with various signal converting functions into an integrated circuit system.
To attain the above first object, an aggregate of semiconductor micro-needles according to the present invention comprises, as their basic structure, a large number of semiconductor micro-needles juxtaposed in a substrate, each of said semiconductor micro-needles having a diameter sufficiently small to cause the quantum size effects.
With the basic structure, the band width of a semiconductor material composing the semiconductor micro-needles is expanded due to the so-called quantum size effects. As a result, the direct transitions of electrons occur even in a semiconductor material such as silicon in which excited electrons make indirect transitions in the proper size to cause the quantum size effects. Consequently, it becomes possible to constitute a light emitting element, wavelength converting element, light receiving element, or the like in which the aggregate of semiconductor micro-needles is disposed by using the photoluminescence and electroluminescence resulting from the quantum size effects of each semiconductor micro-needle, variations in electric characteristics caused by the radiation of light, and the like. In this case, unlike a conventional quantized region composed of silicon with a porous structure or the like, the quantized region according to the present invention is constituted by the aggregate of semiconductor micro-needles, so that the diameter of each semiconductor micro-needle becomes sufficiently small to cause significant quantum size effects and becomes uniform even if the diameter faces any direction in a plane perpendicular to the axial direction.
In the structure of the above aggregate of semiconductor micro-needles, it is preferable that each of the above semiconductor micro-needles is formed substantially perpendicular to the surface of the above substrate and that the above semiconductor micro-needles are formed discretely.
In the above aggregate of semiconductor micro-needles, a protective layer can be obtained by forming an insulating layer on the side portions of the semiconductor micro-needles. In particular, it becomes possible to obtain light from the lateral side of the semiconductor micro-needles by composing the insulating layer of an oxide.
By composing the insulating layer of two layers of an inner oxide layer and an outer nitride layer over the inner oxide layer, it becomes possible to exert a compressive stress on each semiconductor micro-needle without preventing the obtention of light from the lateral side of the aggregate of semiconductor micro-needles, thereby remarkably exerting the quantum size effects.
To attain the above second object, a semiconductor apparatus according to the present invention comprises as its basic structure: a silicon substrate; and a quantized region composed of an aggregate of semiconductor micro-needles, each of said semiconductor micro-needles extending from the surface of the above silicon substrate to a specified depth and having a diameter sufficiently small to cause the quantum size effects.
With the basic structure, there can be implemented a semiconductor apparatus with excellent performance utilizing the remarkable quantum size effects of the aggregate of semiconductor micro-needles described above. Hereinafter, it will be assumed that an electric signal and optical signal input to the quantized region are a first electric signal and first optical signal, respectively, while signals output from the quantized region are a second electric signal and second optical signal, respectively.
The following elements can be added to the basic structure of the above semiconductor apparatus.
It is possible to provide an optical-signal generating means for generating a first optical signal so that the first optical signal is made incident upon the above quantized region and that the above first quantized region receives the first optical signal from the above optical-signal generating means and generates a second optical signal. With the structure, the quantized region functions as an optical converting element.
It is possible to form a trench in a part of the above silicon substrate and to provide the above quantized region and optical-signal generating means on both sides of the above trench, so that they face each other. With the structure, the semiconductor apparatus constitutes a two-dimensional integrated circuit system with an advanced information processing function comparable to a three-dimensional integrated circuit system.
It is possible to provide an upper electrode over the above quantized region so that the upper electrode is electrically connected to the upper end of each of the above semiconductor micro-needles. With the structure, it becomes possible to convert electric signals into optical signals and vice versa via the quantized region.
It is possible to add optical detecting means for receiving the second optical signal generated in the above quantized region and generating a third electric signal.
It is possible to provide the above light detecting means in a portion different from the above quantized region of the above silicon substrate and to compose the above light detecting means of an aggregate of semiconductor micro-needles each having a diameter sufficiently small to cause the quantum size effects.
It is possible to constitute the quantized region of the above basic structure so that it receives a first optical signal and generates a second electric signal and it is possible to provide: optical-signal generating means for generating the above first optical signal so that the first optical signal is made incident upon the above quantized region; and an electric circuit for processing the second electric signal generated in the above quantized region.
It is possible to provide stress generating means for generating a stress in each of the above semiconductor micro-needles in the above quantized region, the above stress being in the axial direction of each of the above semiconductor micro-needle, and to constitute the above quantized region so that it receives the above first electric signal and generates the second optical signal having a wavelength corresponding to the stress in each of the above semiconductor micro-needles. With the above structure, the semiconductor apparatus is provided with a force-to-optical signal converting function. In this case, the force-to-optical signal converting function is particularly enhanced by composing the above stress generating means of the above upper electrode and of a probe connected to the upper electrode so as to transmit a mechanical force from the outside.
The upper electrode of the above basic structure can be made of a transparent material. With the structure, it becomes possible to input the first electric signal to the quantized region without preventing the obtention of the second optical signal from each semiconductor micro-needle in the quantized region in its axial direction.
It is possible to provide on the above upper electrode a condensing means, such as a concave lens, for condensing the second optical signal generated in the above quantized region, which functions as a light-emitting element for generating the second optical signal. It is also possible to divide the above quantized region into a plurality of linearly striped quantized regions in which the aggregate of the above semiconductor micro-needles is formed into linear stripes in a plane parallel to the surface of the silicon substrate, to provide linearly striped discrete layers for separating and insulating the above linearly striped quantized regions so that each linearly striped discrete layer is interposed between any two adjacent linearly striped quantized regions, and to alternately arrange the above linearly striped quantized regions and linearly striped discrete layers so as to constitute a one-dimensional Fresnel lens. It is also possible to divide the above quantized region into a plurality of ring-shaped quantized regions in which the aggregate of the above semiconductor micro-needles is formed into rings in a plane parallel to the surface of the silicon substrate, to provide ring-shaped discrete layers for separating and insulating the above ring-shaped quantized regions so that each ring-shaped discrete layer is interposed between any two adjacent ring-shaped quantized regions, and to alternately arrange the above ring-shaped quantized regions and ring-shaped discrete layers so as to constitute a two-dimensional Fresnel lens.
It is also possible to arrange a plurality of the above quantized regions so as to form a specified flat pattern in the above silicon substrate, thereby constituting the semiconductor apparatus so that it functions as an optical display device.
It is possible to dispose an LSI provided with an additional self-checking circuit on the above silicon substrate and to provide the above quantized region in the self-checking circuit of the above LSI.
Next, to attain the above first object, a method of manufacturing the aggregate of semiconductor micro-needles according to the present invention comprises the steps of: forming on a silicon substrate a dotted mask for covering a large number of dot regions each having a diameter sufficiently small to cause the quantum size effects of the above semiconductor; and etching the above silicon substrate by using the above dotted mask so as to form a large number of semiconductor micro-needles each extending from the surface of the above silicon substrate to a specified depth.
In accordance with the method, there can be formed the aggregate of semiconductor micro-needles which exerts remarkable quantum size effects.
In the step of forming the above dotted mask, it is possible to deposit a large number of granular materials, each having a diameter sufficiently small to cause the quantum size effects of the above semiconductor, directly on the above silicon substrate so that the granular materials constitute the dotted mask. In accordance with the method, the aggregate of semiconductor micro-needles, which is different in structure from the conventional porous semiconductor, can be formed easily. It is also possible, in the step of forming the above dotted mask, to form a photoresist film on the above silicon substrate and then mechanically remove a part of the above photoresist film by means of a probe needle of a cantilever of an atomic force microscope so that the dot regions remain and that the remaining portions of the photoresist film constitute the above dotted mask. It is also possible to apply a photoresist onto the above silicon substrate and then pattern the above photoresist film so that dot-matrix-pattern portions resulting from the interference of light remain and that the above remaining portions of the photoresist film constitute the above dotted mask.
In the step of forming the above dotted mask, it is possible to form an insulating film on the above silicon substrate and to further form a pre-dotted mask for covering a large number of minute dot regions on the above insulating film so that the above insulating film is patterned using the pre-dotted mask and that the remaining portions of the insulating film constitute the above dotted mask.
As the above granular materials, it is possible to use grains of a semiconductor material, metal seeds serving as nuclei for the growth of the grains of a semiconductor material, a  less than 311 greater than -oriented silicon crystal, amorphous silicon, or the like.
After the formation of the above granular materials, it is possible to perform the step of annealing the above granular materials at least once so as to reduce the interface after the formation of the above granular materials. With the annealing step, each of the resulting granular materials presents an excellent configuration closer to a sphere.
Furthermore, in forming the above quantized region, it is also possible to perform the step of forming an insulating layer so as to surround each of the above semiconductor micro-needles. In accordance with the method, it is possible to prevent an impurity from entering into each semiconductor micro-needle as well as discharge the impurity out of the semiconductor micro-needle.
The step of forming the above insulating layer is preferably performed by filling up the space surrounding each of the above semiconductor micro-needles with the insulating layer. The step of forming the above insulating film can also be performed by CVD or by thermally oxidizing the surfaces of the semiconductor micro-needles.
To attain the above second object, a method of manufacturing the semiconductor apparatus according to the present invention comprises the steps of: forming on a silicon substrate a dotted mask for covering a large number of dot regions each having a diameter sufficiently small to cause the quantum size effects of the above semiconductor; etching the above silicon substrate by using the above dotted mask so as to form a large number of semiconductor micro-needles each extending from the surface of the above silicon substrate to a specified depth; removing the above dotted mask; and forming an upper electrode electrically connected to each semiconductor micro-needle over the upper ends of the above semiconductor micro-needles.
In accordance with the method, a semiconductor apparatus with the advanced information processing function as described above can easily be manufactured.
It is possible to further provide the step of forming a p-n junction in the above silicon substrate and form, in the above step of forming an aggregate of semiconductor micro-needles, the semiconductor micro-needles by performing etching to a point at least lower than the above p-n junction. In accordance with the method, a p-n junction is formed in each semiconductor micro-needle, thereby enhancing the quantum size effects.
It is also possible to perform the step of forming a discrete insulating layer which surrounds the above aggregate of semiconductor micro-needles so that the aggregate of semiconductor micro-needles is laterally isolated from other regions. In this case, it is preferable to further perform the step of forming at least one lateral electrode to be connected to the silicon substrate through the above discrete insulating layer. In accordance with the method, it becomes possible to input and obtain an electric signal from the lateral side of the quantized region.